1. Field of the Invention
The present invention relates to a nonwoven fabric fabricated from laminated slit sheet, a method of fabricating such a slit sheet, and a rotary slit forming cutter for fabrication of a slit sheet.
2. Description of the Related Art
A nonwoven fabric can be manufactured by laminating two layers of webs together. A known nonwoven fabric uses a first web comprising a slit sheet having a network structure having generally laterally extending ribbons as if a weft of a woven fabric. The second web may comprise a slit sheet having a network structure having generally longitudinally extending ribbons as if a warp of a woven fabric. Alternately, the second web can be any desired web used as a base layer.
U.S. Pat. No. 4,489,630 discloses a fabrication of such slit sheet. The fabrication of such slit sheet is also disclosed in, for example, Japanese Examined Patent Publication No. 35-10885 and Japanese Unexamined Utility Model Publication No. 64-46193.
The slit sheet is fabricated from a continuous nonporous plastic sheet material by slitting the latter using a rotary slit forming cutter, which has a plurality of cutter edges on the periphery thereof. For fabricating a weft-type slit sheet, the rotary slit forming cutter includes longitudinally spaced rows of cutter edges, each row including a plurality of axially extending cutter edges. For fabricating a warp-type slit sheet, the cutter edges extend circumferentially from the rotary slit forming cutter. The slit sheet can be stretched, before or after the slitting operation, in the direction of the respective slits to strengthen the sheet material and this stretching causes the slits to open and thereby bring the slit sheet into an apertured or fibrillated web having a network structure.
FIG. 9 of the attached drawings shows a laminating process of a weft-type slit sheet or web 1 and a warp-type slit sheet or web 2 for fabricating a nonwoven fabric. The weft-type slit sheet 1 is continuously fed to a laminator 3 according to its longitudinal direction, indicated by the arrow A. It can be seen that the weft-type slit sheet 1 has a network structure having generally laterally extending and longitudinally spaced ribbons 4 and nodes 5 interconnecting longitudinally adjacent ribbons 4. Similarly, the warp-type slit sheet 2 is continuously fed to the laminator 3 according to its longitudinal direction, indicated by the arrow B. The warp-type slit sheet 2 also has a network structure having generally longitudinally extending and laterally spaced ribbons 6 and nodes 7 interconnecting ribbons 6.
The nonwoven fabric, comprising the lamination of the weft-type and warp-type slit sheet 1 and 2, is a continuous web and wound in the form of a roll. FIG. 8 of the attached drawings shows a roll of the nonwoven fabric 8. As shown in FIG. 8, a problem arises in the nonwoven fabric 8 that the peripheral surface of the nonwoven fabric 8 is corrugated and includes bulges 9. The corrugated peripheral surface of the nonwoven fabric 8 involves a problem that partial slack areas arise in the web of the nonwoven fabric 8 when it is unwound, for example, for further laminating the nonwoven fabric 8 with a further web, or processing it to manufacture products. When the unwound nonwoven fabric 8 is wound again, wrinkles arise in the nonwoven fabric 8. To avoid these problems, the nonwoven fabric 8 must be wound in a small roll.